Find First Non-Repeating Character in a String

Find first non-repeating character in a string

Find first non-repeating character in a string

Given an input string, Write a code to find first Non-repeating character in a string. Suppose an input string is webrewrite, the first non-repeated character in this string is b.

In this tutorial, we will write a code in multiple programming languages to solve this problem.

How to Find First Non-Repeating Character in a String

Method 1 – Naive Approach

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Use two for loops and compare each character with every character of a string.  But the time complexity using this approach is  O(n2).

Method 2 – Create key and value pairs for character and it’s count

We can create a key and value pairs for character and it’s count. This approach is much better as compared to first one. Let’s implement this method.

PHP Code to Find First Non-Repeating Character in a String

Let’s try to solve this problem in a single traversal.

Method 2:

How to sort string in PHP.

C++ Program Find First Non-Repeating Character in a String

In this code, I am using C++ map library to make a hash (key and value pair).

Question on Linked List.

 

Java Program to Find First Non-repeating character in a String

 

Conclusion

If you know some other efficient way to solve this problem then let us know through your comments.

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